However, while not aided by the above-average length of the Spa-Francorchamps lap, Russell's gap to first place in Q1 in Belgium was his biggest all season - with a high level of drag compromising the FW42's performance at the top speed-dependent venue.

And with Monza the weekend after placing an even higher premium on straightline performance than Spa, Russell said he was gearing up for a particularly difficult Italian Grand Prix.

"In all honestly, it's probably an even harder weekend than Spa," Russell said. "Everybody knows we're struggling with downforce, but probably not a lot of people know that we have an incredible amount of drag on the car as well, incredibly slow in the straights.

"[At Spa] we were up to two seconds slower on the straight versus the quickest cars, a second slower in the straight versus anyone else. So it was incredibly difficult for us.

"And I think that was clear - after Hungary, obviously a very good performance, but a lot of that was due to the lack of straights in Hungary. It being all corners, the deficit didn't seem as great.

"Yeah, this is probably going to be the toughest one of the year."

Teammate Robert Kubica said Spa had proven as difficult for Williams as expected, with "no bad or good surprises", and conceded that "it probably will not get better or easier" at Monza.

"I think the gap will be smaller because Monza is generally the track where the gaps are smaller, but for our top speed and our drag, it will not change a lot," he said."

Williams had introduced a significant update to its FW42 in Germany before the summer break, and while it provided substantial downforce gains, these look to have come at a cost for the car's aerodynamic efficiency.

Russell said the drag problem "was already there" before the update, but added: "We've probably got very slightly more now - but obviously much more downforce than we had before Hockenheim."